5.3.2 Fundamental Particles

(a) explain that since protons and neutrons contain charged constituents called quarks they are, therefore, not fundamental particles

Stowmarket Physics Fundamental particles Until mid-20 th century, it was though that all atoms consisted of electrons, protons and neutrons Due to the increasing sophistication of the particle accelerator, and increased sensitivity of equipment measuring cosmic rays, more and more particles were being discovered Eventually, this “particle zoo” was arranged in a more orderly way

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Video Fundamental Particles CERN Standard model

(b) describe a simple quark model of hadrons in terms of up, down and strange quarks and their respective antiquarks, taking into account their charge, baryon number and strangeness;

Stowmarket Physics Simple model Atom Hadrons Leptons Electrons Neutrinos Protons Neutrons Quarks Affected by the strong nuclear force Not affected by the strong nuclear force

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(d) describe the properties of neutrons and protons in terms of a simple quark model

Stowmarket Physics Properties of neutrons and protons ProtonNeutron u d d u u d

Stowmarket Physics Properties of neutrons and protons Proton uud total charge = ⅔ + ⅔ - ⅓ = 1 Neutron udd total charge = ⅔ - ⅓ - ⅓ = 0

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(e) describe how there is a weak interaction between quarks and that this is responsible for β decay

Stowmarket Physics β decay Nucleus is held together by the strong nuclear force This explains α decay, but not β decay There is another force, the weak interaction or weak nuclear force Acts on quarks and leptons Responsible for β decay

(f) state that there are two types of β decay (i) state that a β - particle is an electron and a β + particle is a positron

Stowmarket Physics β decay There are two types of β decay: Beta-minus (β - ) electron negative charge –e Beta-plus (β + ) positron positive charge +e

(g) describe the two types of β decay in terms of a simple quark model; (h) state that (electron) neutrinos and electron) antineutrinos are produced during β + and β - decays, respectively

Stowmarket Physics β - decay In β - decay a neutron is changed into a proton, in other words udd changes into uud. A d changing to a u can only happen through the weak interaction. Electron Anti-neutrino

Stowmarket Physics β + decay In β + decay a proton is changed into a neutron, in other words uud changes into udd. A u changing to a d can only happen through the weak interaction. Electron neutrino